1. Technical Field
This invention relates to novel sterol esters of conjugated linoleic acids and a process for the production of the same by esterification of sterols and stanols with a conjugated linoleic acid.
2. Background
It is known that the addition of plant sterol (phytosterol) to diets will reduce serum cholesterol levels. Such additives effect the reduction of serum cholesterol through the disruption of intestinal absorption of dietary cholesterol by displacing it from bile and micelli. Free sterols or stanols, though, are not optimum candidates for use in typical pharmaceutical or dietary dosage forms as cholesterol reducing agents due to their very high melting points 130 C. and low solubility in aqueous and oil media. As a result such compounds are preferred to be converted into their fatty esters for food applications, which reduce their melting points and solubility in oil. However, the fatty acids attached to sterol in the current commercial products are from vegetable oil such as sunflower, canola, or soybean oil. Those fatty acids provide no pharmaceutical or nutraceutical functions except increasing the total calories of the products.
Conjugated fatty acids are known to have many health benefits such as reducing body fat, inhibiting tumor growth and reducing atherosclerosis. Such conjugated fatty acids are naturally found in beef and dairy fats in trace amounts (0.2-30 mg/g food). One such conjugated fatty acid is conjugated linoleic acid (octadecadienoic acid), hereinafter referred to as CLA. Cattle convert the linoleic acid in grass into CLA by their special digestive processes. However, since humans cannot produce such conjugated fatty acids, such additives to the human system must be through the diet. Thus the providing of CLA in a form to permit its use in dietetic foods would serve as a significant contribution to the field of dietetic foods since it would enable the recipient to receive a valuable additive since it is known that CLA is effective in increasing body protein or preventing the loss of body protein in a human, increasing food efficiency in humans and assists in reducing body fat.
It is thus an object of the present invention to provide a novel ester composition consisting essentially of phytosterols including plant sterols/stanols and conjugated linoleic acids.
Another object of this invention is to prepare sterol and stanol esters of CLA for their utilization in food and dietary supplement products.
Another object of the present invention is to provide a process for the production of sterol esters of conjugated linoleic acids through transesterification and/or esterification.
In accordance with one embodiment of the present invention, I have discovered that through the esterification of a sterol or stanol with a conjugated fatty acid, such as CLA, there is provided a compound which provides the advantages of both the conjugated fatty acid and the sterol or stanol. CLA is a liquid fatty acid with two conjugated double bonds, therefore, it can reduce the melting point of sterols and stanols dramatically. Indeed, the beta-sitosterol ester of CLA is liquid at ambient temperature while the current commercial products made of the fatty acids derived from vegetable oils are solid or semisolid. The sterol ester of CLA also provides a product having lower total calories than the blended product that provides the same doses of sterol and CLA. Such new products thus offer the combined benefits of sterols/stanols as a cholesterol control agent and CLA as an anticarcinogen and fat reducing agent. Such esters can be used as a supplement or ingredient in foods.
In accordance with another embodiment of the present, sterol esters can be readily prepared through esterification of sterol or stanol with the conjugated fatty acid or by transesterification of sterol or stanol with of the conjugated fatty acid methyl ester. Transesterification is the preferred method to those skilled in the art.
A better understanding of the present invention, its several aspects, and its advantages will become apparent to those skilled in the art from the following detailed description, wherein there is shown and described the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated for carrying out the invention.
As used herein the term xe2x80x9csterol esterxe2x80x9d includes both the plant sterol ester per se as well as the hydrogenated sterol products which are referred to as stanol and campestanol. Such compounds have the following general formula:
Acxe2x80x94COxe2x80x94Oxe2x80x94ST
wherein Acxe2x80x94CO is an acyl group from a conjugated fatty acid and Oxe2x80x94ST is a steryl group derived from a sterol/stanol.
The term xe2x80x9cconjugated fatty acidxe2x80x9d is intended to refer to conjugated linoleic acid (CLA) which in turn refers to a group of geometrical and positional isomers of linoleic acids including but not limited to 9,11-octadecadienoic acid, and 10-12 octadecadienoic acid. The cis-9, trans-11 isomer is the most dominant isomer of CLA in dairy products and is also the most biologically active form as known at present.
The term xe2x80x9csterolxe2x80x9d or xe2x80x9csterol/stanolxe2x80x9d as used herein is intended to mean the sterol compound per se or its hydrogenated form including stanol and campestanol.
The present invention is based upon my discovery that through the use of the conjugated fatty acidxe2x80x94CLAxe2x80x94in the esterification of a sterol there is obtained a product which is liquid at ambient temperature and which product has lower total calories and which product provides the combined benefits of cholesterol control agent and an anticarcinogen and fat reducing agent.
The present invention provides a process for esterfying stanols or/and sterols with CLA. This esterification reaction may be accomplished either through the reaction of the sterol with CLA using a esterification catalyst such as sulphonic acids and tin chloride or though the reaction of the sterol with CLA methyl ester using a transesterification catalyst such as sodium methoxide and hydroxide. The results of those esterification reactions is a sterol ester of CLA or a stanol ester of CLA.
While any stanol or sterol that is functionalized with a hydroxy group is suitable for transesterification and esterification by the processes as described herein, in one presently preferred embodiment of the present invention there is utilized a sterol/stanol selected form the group consisting of beta-sitosterol, campesterol, stigmasterol and sitostanol. Other suitable sterols include but not limited to brassicasterol, avenasterol, alpha-spinasterol and ergosterol. It is understood that those sterols/stanols for esterifying may be used in pure form or mixed in certain ratios.
Likewise while any isomer of a conjugated linoleic acid is suitable for esterification by the process as described herein, in one presently preferred embodiment of the present invention there is utilized a conjugated linoleic acid selected from the group consisting of cis-9, trans-11-conjugated linoleic acid and trans-10, cis 12-conjugated linoleic acid.
The acid-catalyzed esterification reaction of sterol with CLA and base-catalyzed transesterification reaction of sterol with CLA methyl ester, respectively, are depicted below demonstrating the formation of a sterol ester of CLA per the present invention. As shown in the reaction mechanism on the left sterol is reacted with CLA in the presence of an acid catalyst to produce sterol ester of CLA. In the reaction mechanism on the right (which represents the preferred mechanism), sterol is reacted with CLA methyl ester to produce sterol ester of CLA in the presence of a base catalyst. 
R is defined as following alkyl or alkenyl groups:
beta-Sitosterol: xe2x80x94CH(CH3)CH2CH2CH(C2H5)CH(CH3)2
Stigmasterol: xe2x80x94CH(CH3)CHxe2x95x90CHCH(C2H5)CH(CH3)2
Campesterol: xe2x80x94CH(CH3)CHxe2x95x90CHCH(CH3)CH(CH3)2 (no double bond at 5, 6)
Brassicasterol: xe2x80x94CH(CH3)CHxe2x95x90CHCH2CH(CH3)2
Avenasterol: xe2x80x94CH(CH3)CH2CH2C(xe2x95x90CHxe2x80x94CH3)CH(CH3)2 (double bond at 5, 6 or 7, 8 only)
alpha-Spinasterol: xe2x80x94CH(CH3)CHxe2x95x90CHCH2C(C2H5)CH(CH3)2(double bond at 7, 8)
Ergosterol: xe2x80x94CH(CH3)CHxe2x95x90CHCH(CH3)CH(CH3)2 (double bonds at 5, 6 and 7, 8)
A similar reaction system is carried out when the hydrogenated sterol such as stanol is the reactant.
The molar ratios of the starting materials for the transesterification and esterification reactions are provided in stoichiometric levels. It is preferred that the CLA be present in at least 5-10% excess so as to react with all of the sterol or stanol. Any excess unreacted CLA is easily removed in the product work-up.
The usage of esterification catalyst varies with the catalyst used and their uses are reviewed in Bailey""s Industrial Oil and Fat Products, 4th edition, edited by Daniel Swern, Volume 2, PP 113-127. Since esterification involves high reaction temperature and low reaction rate, sterol ester of CLA are preferred to be prepared via transesterification.
In carrying out the process of the present invention solvents such as ethers and short chain alkanes may be added to the reaction mixture to promote reaction.
The reaction rate of transesterification increases at an elevated temperature. The typical reaction temperature ranges from 40 C. to about 250 C. The reaction period may vary widely, but as a general practice a reaction time in the range of about 4 to about 20 hours can be utilized. The reaction is normally carried out for a time which will permit the reaction to go to completion so that the sterol or stanol present is completly esterified. Normally the ester product is obtained in yields of greater than 95%.
Following completing of the reactions, the resulting ester product can be isolated with or without organic solvent extraction after removing the catalyst such as by water washing. Typical solvents are low boiling point organic compounds including but not limited to diethyl or petroleum ethers, hexane, dichloromethance, chloroform, and toluene.